Shelf assemblies are often used to house printed circuit boards (PCBs) also referred to as cards. The printed circuit boards are inserted into a card cage assembly engaging a perpendicularly oriented backplane that is also a printed circuit board. Proper engagement provides electrically conductive paths that connect circuits between or among removable printed circuit boards. The card cage and backplane assembly make insertion and extraction of printed circuit boards simple for purposes of replacement, service, etc. Slots in the card cage assembly hold the inserted printed circuit boards in place. In addition, pin connectors at specific locations on the backplane also ensure engagement of the printed circuit boards with the backplane. Because pin connector locations are specific, a volumetric limit is imposed on each removable printed circuit board thus limiting the size of a printed circuit board that can be inserted in a given backplane slot.
Certain applications require "sparing" of circuits to ensure that critical equipment remains functional even in the case of a fault. A fault could occur on a communication access port, processor complex, or other critical resource. Often the single slot practice of sparing or "1:1 or 1+1 protection" is used to ensure that the process continues without an interruption of service. Pairing certain printed circuit board assemblies provides the redundancy needed to support these critical functions.
What is needed is a backplane arrangement that can support insertion of printed circuit boards wider than a single slot while maintaining specific connections between or among slots so that printed circuit boards of varying slot width can be paired with respect to one another.